ViewPager切换动画PageTransformer使用

来自： http://www.jcodecraeer.com//a/anzhuokaifa/androidkaifa/2014/0814/1650.html

Android从3.0开始，就添加了很多动画，ViewPager当然也不例外，相对于非常平庸的默认切换动画，Google给我们展示了两个动画例子：DepthPageTransformer和ZoomOutPageTransformer，实际上我们也可以通过实现ViewPager.PageTransformer来做出完全不同的切换动画效果。关键是要理解transformPage(View view, float position)的参数。view理所当然就是滑动中的那个view，position这里是float类型，不是平时理解的int位置，而是当前滑动状态的一个表示，比如当滑动到正全屏时，position是0，而向左滑动，使得右边刚好有一部被进入屏幕时，position是1，如果前一页和下一页基本各在屏幕占一半时，前一页的position是-0.5，后一页的posiotn是0.5，所以根据position的值我们就可以自行设置需要的alpha，x/y信息。

下面，我们来看看Google官方提供的两种动画效果的代码，很简单，相信每个人看过之后，都能自己实现一种动画效果，

DepthPageTransformer：

public class DepthPageTransformer implements PageTransformer {      private static float MIN_SCALE = 0.75f;                                 @SuppressLint("NewApi")      @Override      public void transformPage(View view, float position) {          int pageWidth = view.getWidth();          if (position < -1) { // [-Infinity,-1)                                  // This page is way off-screen to the left.              view.setAlpha(0);          } else if (position <= 0) { // [-1,0]                                      // Use the default slide transition when                                      // moving to the left page              view.setAlpha(1);              view.setTranslationX(0);              view.setScaleX(1);              view.setScaleY(1);          } else if (position <= 1) { // (0,1]                                      // Fade the page out.              view.setAlpha(1 - position);              // Counteract the default slide transition              view.setTranslationX(pageWidth * -position);              // Scale the page down (between MIN_SCALE and 1)              float scaleFactor = MIN_SCALE + (1 - MIN_SCALE)                      * (1 - Math.abs(position));              view.setScaleX(scaleFactor);              view.setScaleY(scaleFactor);          } else { // (1,+Infinity]                      // This page is way off-screen to the right.              view.setAlpha(0);                                     }      }                             }

ZoomOutPageTransformer：

public class ZoomOutPageTransformer implements PageTransformer {      private static float MIN_SCALE = 0.85f;                         private static float MIN_ALPHA = 0.5f;                         @Override      public void transformPage(View view, float position) {          int pageWidth = view.getWidth();          int pageHeight = view.getHeight();                             if (position < -1) { // [-Infinity,-1)                                  // This page is way off-screen to the left.              view.setAlpha(0);          } else if (position <= 1) { // [-1,1]                                      // Modify the default slide transition to                                      // shrink the page as well              float scaleFactor = Math.max(MIN_SCALE, 1 - Math.abs(position));              float vertMargin = pageHeight * (1 - scaleFactor) / 2;              float horzMargin = pageWidth * (1 - scaleFactor) / 2;              if (position < 0) {                  view.setTranslationX(horzMargin - vertMargin / 2);              } else {                  view.setTranslationX(-horzMargin + vertMargin / 2);              }              // Scale the page down (between MIN_SCALE and 1)              view.setScaleX(scaleFactor);              view.setScaleY(scaleFactor);              // Fade the page relative to its size.              view.setAlpha(MIN_ALPHA + (scaleFactor - MIN_SCALE)                      / (1 - MIN_SCALE) * (1 - MIN_ALPHA));          } else { // (1,+Infinity]                      // This page is way off-screen to the right.              view.setAlpha(0);          }      }  }

有了这两种效果，我们在代码中设置一下就生效了：mPager.setPageTransformer(true, new DepthPageTransformer());

下面是效果图：第一张是DepthPageTransformer效果，第二张是ZoomOutPageTransformer效果。

OK，最后奉上源代码：http://download.csdn.net/detail/weidi1989/6443601